This is a P40 resource proposal to maintain and expand the Xiphophorus Genetic Stock Center (XGSC), and enhance services provided to research investigators. Xiphophorus is a small freshwater, aquarium fish that has been extensively used in carcinogenesis studies, but also used as a model organism in a variety of different fields of study that transcends several NIH institutes. The XGSC has operated within the United States for over 70 years. The proposed initiatives will greatly enhance the usability of the Xiphophorus model system for research scientists using this system, but also for "non-Xiphophorus" scientists that envision application of the powerful genetics provided by this model system. The traditional strength of this model involves the non-biased assessment of genetic variability among Xiphophorus species (22 known taxa), and capability of producing fertile interspecies hybrids, allows chromosomal/marker inheritance to be followed in individual backcross hybrid progeny. Complex traits, such as susceptibility to the development of neoplastic disease, or behavioral characteristics, can be studied using Xiphophorus, and underlying genetic factors can be identified. Since research using these fishes is currently expanding within the scientific community, it is timely to enhance the services offered by the Xiphophorus Genetic Stock Center. We propose: 1) To preserve and enhance the Xiphophorus Genetic Stock Center and provide the research community with animals from genetically managed lines in large numbers according to the specifications of each investigator. 2) To establish and maintain extensive and flexible computer databases of fish, and derived samples. These databases will be made available for scientific use. Links and information regarding fish maintenance, current research projects and other XGSC information will be provided via the xiphophorus.org web- site. 3) To continue saturation of the Xiphophorus gene map and development of technologies providing investigators with efficient molecular tools necessary to use this powerful genetic system to approach complex scientific questions, and 4) To establish technology allowing cryopreservation of Xiphophorus sperm samples and thereby provide a preservation program where the XGSC maintains the genetic heritage of all Xiphophorus strains and species.